Studies of the Cytochrome C1 Subunit of the Cytochrome Bc1 Complex from Rhodobacter Sphaeroides

Abstract

The cytochrome c1 of Rhodobacter sphaeroides bc1 complex contains several insertions and deletions that distinguish it from the complex of other higher organisms. Additionally, it contains two non-conserved cysteins, C145 and C169. The orientation of the insertions and the state of these non-heme binding cysteins remain unknown. Mutating one or both cysteins is found to have comparable effects on the functionality of the cytochrome bc1 complex. Mutants show decreased activity but can still support a delayed photosynthetic growth. The mutated cytochrome c1 has a decreased Em, without any alteration in the heme ligation environment, caused by a structural modification in the head domain of cytochrome c1. Analysis of the mutants reveals that the two cysteins form a disulfide bridge. Cleavage of cytochrome c1 between the two cysteins followed by gel electrophoresis show two fragments only under reducing conditions confirming the existence of a disulfide bridge. The disulfide bridge is essential in maintaining the structural integrity of cytochrome c1 and thus the functionality of the cytochrome bc1 complex